There are various known techniques for processing and digitally altering video images which may be used, for example, in ‘post production’ processes to add special effects to video, to remove defects or unwanted objects from video, or the like. Some known automatic techniques map points on a video image by tracking camera movement and using the tracking data to produce point clouds. More detailed models can be built using interactive tools which aid the recovery of polyhedral surface models (which are also known as surface meshes) from video. Point clouds and surface models can then be used to alter the video footage. However, if the video footage includes non-rigid scenes, for example, deformations in objects such as those exhibited by a talking face, this can prevent an accurate model from being formed.
The embodiments described below are not limited to implementations which solve any or all of the disadvantages of known video processing techniques.